High frequency amplifier



W. J. POCH HIGH FREQUENCY AMBLIFIER Dec. l2, 1939.

2 Sheets-Sheet l Filed March 28, 193e -J l-illih Dec. 12, 1939. l w. J. POCH 2,183,203

HIGHk FREQUENCY AMPLIFIER Filed Maron 28, 1936 2 sheets-sheet 2 Patented Dec. 12, 1939 UNITED STATES PATENT OFFICE HIGH FREQUENCY .IHVIPLIFIERy tion of Delaware Application March 28, 1936, Serial No. 71,364

1 Claim.

My invention relates to high frequency ampligers and particularly to television receiver ampliers.

It is often desirable to vary the frequency response characteristic of an amplifier. In television receiver amplifiers, especially, it is desirable that they be adjustable for the purpose of varying the relative amplification of the high frequency components of an incoming picture signal. It may also be desirable in some instances to vary the relative phase of different frequency components of a signal.

In my Patent No. 2,122,990, which is assigned to the Radio Corporation of America, I describe and claim a television receiver having adjustable means for varying its frequency response characteristic. In that application I point out that if a television receiver is tuned away from lone transmitter station to a second transmitter station which transmits more high frequency components of a picture signal than the first transmitter, the picture at the receiver will have a bas-relie appearance.l To overcome this, the receiver must be adjusted to amplify the higher frequency components to a less degree.

On the other hand, if the receiver is tuned back to thefirst transmitter station, it is desirable to increase the high frequency response of the receiver vso that the picture will contain a maximum of detail. There are various other reasons for making the high frequency response of a television receiver adjustable. For-example, if there is considerableinterference, a picture may be improved by lowering the high frequency response whereby noise in the picture is reduced. As interference or "noise is generally at the higher frequencies, the loss of detail inv a `picture is often less objectionable than the noise included at these frequencies.

It is an object of my invention to provide an improved method of and means for varying the frequency response characteristic of an amplifier. A further object of my invention is to provide an improved method of and means for controlling ythe degree of ampliiicationfof the high frequency components of a signal as compared with the amplification of its low frequency components.

A further` object of my invention is to provide v an. improved method of and means for controlling the amplification and/or phase of the high frequency components of a signal as compared v'vviththe amplification and/or phase of its low frequency components.

A still further object of my invention is to provide an improved television receiver.

In a preferred embodiment of my invention the picture signal is supplied from an amplifier tube to the input circuits of two amplifier channels, one channel being designed to amplify all components of the picture signal a fixed amount, and the other channel being designed to amplify the high frequency components substantially to the exclusion of the low frequency components. 10,.

The two amplifier channels have a common output circuit whereby their outputs add to give the desired resultant picture signal. The second channel includes adjustable means for determining the amount the high frequency coml5;

ponents are amplified whereby the high frequency content of the resultant signal may be controlled.

Other objects, features, and advantages of my invention will appear from the following descrip- 2p tion taken in connection with the accompanying drawings in which i Figure l is a circuit diagram of a television receiver amplifier embodying my invention, and

Figs. 2 and 3 are circuit diagrams of other ein- 25 bodiments of my invention.

Referring to Fig. 1, my invention is shown applied to a television receiver which may include a heterodyne receiver portion indicated at I. This portion of the reeciver preferably includes an 30 automatic volume control circuit for supplying a signal constant amplitude to the first video amplifier tube 2. The amplifier tube 2 may be of the screen grid type having a cathode 3, a control grid 4, a screen grid 6 and a plate 1. A grid 35 biasing battery 8 or other suitable voltage source The variable tap I2 may be o supplied through a coupling condenser I4 to the 45 control grid 4.

A suitable positive potential is supplied through Aa filter resistor I6, a peaking coil I1 and a plate resistor I8 to the plate 1 of the amplifier tube 2.

The filter resistor I6 is shunted by the usual 50 filter condenser I9.

The picture signal appearing in the output circuit of the amplifier tube 2 is supplied to two amplifier channels 2| and 22. The first channel 2| includes Aanamplifier tube 23 which may be of 55 the three-element type having a cathode 24, a control grid 26 and a plate 21. The control grid 26 is maintained at a suitable negative bias by suitable biasing means such as a biasing battery 28, the grid 26 being connected through a grid resistor 29 and the biasing battery 28 to the cathode 24. Picture signal is supplied to the control grid 26 through a coupling condenser 3I which is connected between the plate 1 of the amplifier tube 2 and the control grid 26. It will be noted that the input circuit of the amplifier tube 23 is thus connected across both the plate resistor I8 and the peaking coil I1 whereby all picture signal components are supplied thereto with substantially equal amplitude.

A suitable positive potential is supplied to the plate 21 of the amplifier tube 23 through a filter resistor 32, a peaking coil 33, a plate resistor 34 and a second resistor 36. The filter resistor 32 is by-passed by the usual filter condenser 31.

The resistor' 85 is provided between the plate 21 and the plate resistor 34 for two reasons. In the first place, it lowers the gain of the tube 23 a certain amount so that more effective control is provided by the tube 42. In the second, and more important, place it reduces the high frequency response of the channel 2I whereby it is possible by actuation of the control knob 53 to vary the combined high frequency response of the two channels 2| and 22 from a value which is too low to one which is too high. The resistor 36 causes loss of highs for the reason that the tube electrode capacities are between ground the junction point of resistors 34 and 36. It may be mentioned, by way of example, that the resistor 36 may have a value of 10,000 ohms and the resistor 34 a value of 6,000 ohms.

The picture signal appearing across the plate resistor 34 and peaking coil 33 is supplied to an output tube 38 which, in turn, supplies the picture signal to the control grid 39 of the cathode ray receiver tube 4 I. The grid condenser 40 and grid resistor 45 are given suitable values to provide automatic background control as described and claimed in my application Serial No. 718,192, filed March 30, 1934, and assigned to the Radio Corporation of America.

The second channel 22 includes an amplifier tube 42 which may be of the screen grid type, having a cathode 43, a control grid 44, a screen grid 46, and a plate 41. Suitable variable bias means is provided, this being a biasing battery 48 which is shunted by a potentiometer 49 in the particular circuit illustrated. The control grid 44 is 4connected through a grid resistor 5I and a variable tap 52 to a point on the potentiometer 49. As inthe case of the first described amplifier tube 2, the variable tap 52 may be moved along the potentiometer 49 by rotating a knob indicated Aat 53 which is located -on the receiver panel.

In one embodiment of my invention the input circuit of the amplifier tube 42 is not connected across the entire output circuit vof the lamplifier tube 2,`but, instead, is connected across the peaking coil I1 only. This connection is from the control grid 44 through a coupling condenser 54, a switch arm 50 and a switch contact point '51 to the junction point of the peaking coil I1 and the .plateresistor I8. It will be evident that the signal appearing across Ithe peaking coil I1 has the high frequency components of the picture signal accentuated since the ,peaking coil presents a higher impedance to high frequencies than to .low frequencies and that, as .a result, the picturesignal supplied to the input circuit ofthe amplifier tube 42 includes substantially only the higher frequency components.

In a preferred embodiment, the plate 41 of the amplifier tube 42 is connected to the plate end of the plate resistor 34, this connection being through a switch arm 58 and a switch contact point 59 in the circuit illustrated. It will be seen that the amplifier tubes 23 and 42 have a common output circuit whereby their outputs are added to give a signal which is the sum of the complete picture signal supplied to the first channel 2| and the high frequency signal component supplied to the second channel 22.

By moving the variable tap 52 along the potentiometer 48, the gain of the amplifier tube 42 may be varied whereby the amount of high frequency signal supplied to the common output circuits is varied to control the high frequency content of the picture signal supplied to the output tube 38.

The television receiver is provided with a suitable separating circuit indicated at GI which separates picture signals from synchronizing signals. The horizontal synchronizing signals and the vertical synchronizing signals are supplied from the circuit 6I to deiiecting circuits 62 and 63, respectively. Deflecting coils 64 and 66 are supplied with saw-tooth deflecting currents from the deflecting circuits 62 and 63, respectively, for scanning a fluorescent screen at the end of the cathode ray tube 4 I.

Other circuit connections than those described above may be employed. For example, the switch arm 58 may be moved to the dotted line position to make the contact with a switch Contact point 61 whereby the plate 41 is connected to the junction point of the peaking coil 33 and the plate resistor 34. If the other switch 56 is left in the solid line position shown on the drawings, the high frequency components of the picture signal will be accentuated more than when the amplifier is connected as first described. This is apparent from the fact that when the plate 41 is connected to the junction point of the peaking coil 33 and the plate resistor 34, the plate circuit of the amplifier tube 42 is almost purely inductive whereby the plate impedance of the tube is much greater for high frequencies than for low frequencies. Consequently, the 'amplifier tube will amplify the higher frequencies the greater amount.

Substantially the same results as those obtained by the rst described connection may be obtained by throwing switches 56 and 58 to the dotted line positions. The operation of the circuit connected in this way will be understood from the foregoing description. All picture signal components are supplied to the two amplifier channels 2I and 22 without discrimination but the amplifier in the channel 22 amplifies the high frequency components more than the low frequency components, whereby it accentuates the high frequency components in the resultant picture.

Referring to the amplifier circuit shown in Fig. 2, it differs from the circuit shown in Fig. 1 mainly in the manner in which the amplifier channel 22 is designed for the purpose of accentuating the high frequency components of the picture signal. In the two figures, like parts are indicated by the same reference numerals. In the circuit shown in Fig. 2, the input circuit of the amplifier tube 42 in the channel 22 is coupled to the output circuit of the amplier 2 through a coupling condenser 'II having such small capacity that it presents a high impedance to the low frequency components of the picture signal. Therefore, more high frequency components than llow frequency components are supplied to the ampli-` fier 42, whereby the output of the amplifier accentuates the high frequency content of the resultant picture signal.

It is preferred to accentuate the high frequency components still further by providing an inductance coil 12 adjacent to the control grid` 44, this coil having the proper amount of inductance to make it resonate With the input capacity of the amplifier tube 42 at the highest frequencies. This causes further accentuation of the high frequency components.

Various other designs may be employed for the purpose of accentuating the high frequency corn ponents of the picture signal in the amplifier channel 22. For example, in Fig. 3, where parts similar to those in Fig. 1 are indicated by like reference numerals, the picture signal is supplied from the output circuit of the amplifier 2 to the input circuit of the amplifier 42 through a highpass lter 13 consisting of a plurality of sections, each including a series condenser 'i4 and a shunt resistor 16.

Experience has indicated that it is desirable to advance the phase of the high frequency components of a picture signal with respect to the low frequency components. This can be accomplished by inserting a delay network Tl between the amplifier 2 and the amplifier 23 of the first channel 2| whereby all frequency components of a picture signal are delayed substantially the same amount. The high frequency components which appear in the output circuit of the amplier 42 of the second channel 22 are not delayed and, therefore, in effect are advanced in phase with respect to the signal supplied by the first amplier channel. It will be apparent that when the outputs of the two amplifier channels are cornbined, the resultant signal includes high frequency components which have been advanced in phase with respect to the low frequency components.

It will be understood that the two amplifier tubes 23 and 42 in the two channels may be included in a single envelope, this being 'the preferred arrangement. In one amplifier embodying my invention, a 6F7 tube was employed, the triode part of this tube acting as the amplifier 23 and the pentode part acting as the other amplifier 42.

While I have illustrated and described only two amplifier channels connected in parallel for varying the frequency response curve of the complete amplifier, three or more such amplifier channels may be employed. For example, a third channel may be designed to amplify the low frequency components of a picture signal more than the other components whereby both the high frequency response andthe low frequency response of the television receiver may be adjusted for the purposes described in my above-mentioned Patent No. 2,122,990.

It will be apparent from the foregoing description that various other modifications may be made in my invention without departing from the spirit and scope thereof', and I desire, therefore, that only such limitations shall be imposed thereon as shall be necessitated by the prior art and are set forth in the appended claim.

I claim as my invention:

In combination, an amplifier tube having a grid circuit and a plate circuit and adapted to am: pli-fy signals comprising components covering a wide frequency range, a plurality of amplifier channels each having anrinput circuit coupled to said plate circuit, one of said amplifier channels including an ampliertube having a plate circuit which includes a peaking coil and a plate resistor in series with said resistor located between said coil andthe plate of said tube, the other of said amplifier channels including an amplifier tube having a plate, and means for connecting said plate to the junction point of said coil and said resistor whereby the outputs of said amplifier channels add with the second amplifier channel amplifying the high frequency components more than the lower frequency components.

WALDEMAR J. POCH. 

